1. Field of the Invention
The present invention relates to clock pulse generators operating in a subnanosecond period range.
2. Description of the Prior Art
Precise interval measurements are essential in nuclear and ballistic time-of-flight tests, radar ranging and in the characterization of active components, such as integrated circuits. For a detailed discussion of time interval measurements, reference is made to "Measure Time Interval Precisely," by David Martin, Electronic Design, vol. 24, Nov. 22, 1974, pp. 162, et seq. Digital signal processing equipment for making such interval measurements desirably utilizes a pulse train circuit, startable on command, producing short duration pulses with accurately controlled interpulse spacing. One such pulse train circuit utilizing transferred electron logic devices (TELD) is described in U.S. Pat. No. 4,000,415 issued Dec. 28, 1976, to the instant inventor and assigned to the common assignee.
The two terminal transferred electron device (TED), known as a Gunn-Effect Device, and the three-terminal transferred-electron logic device (TELD), known as a Schottky-Barrier Gate Gunn-Effect Digital Device are well known.
TED's and TELD's have a negative resistance over a frequency range which is essential to the present invention as described in detail below. For further details on the negative conductance properties of TELD's reference is made to "Multifrequency Operation of a Quenched-Domain Mode Gunn-Effect Device," by W. R. Curtice and D. D. Khandelwal, Proceedings of the IEEE, vol. 59, No. 3, March 1971, pp. 416-417.
A gate terminal, an anode terminal, and a cathode terminal comprise the three terminals of a TELD. Typically, current is conducted from the anode to the cathode. When a voltage between the anode and the gate exceeds a threshold voltage, an electron charge depletion region followed by an electron charge accumulation region forms and migrates from the gate to the anode in a period of time known in the art as a transit time period. The reciprocal of the transit time period of a TELD in a resistive circuit is the device's natural transit-time frequency. The depletion region and the accumulation region are collectively referred to as a dipole domain. The formation of the dipole doamin causes the current to decrease.
When the domain has migrated to the anode, the current increases. When the threshold voltage is maintained to sustain the formation of mobile domains, the TELD oscillates.
The anode-gate threshold voltage is determined by voltages applied to the anode and the gate with respect to the cathode, the geometry of the TELD, and the material constants. For a more detailed description of TELD's reference is made to "Threshold Condition of Schottky-Gate-Gunn Pulse Device," Y. Utsugi, et al., Review of the Electrical Communication Laboratories, volume 23, Nos. 3-4, March-April, 1975, pages 279, et seq.
TELD's have been utilized in the construction of high speed pulse train generators. For a discussion of prior art pulse train generators, reference is made to "Characteristics and Applications of a Schottky-Barrier-Gate Gunn-Effect-Digital Device," by Sugeta, et al., IEEE Transactions on Electron Devices, volume ED-21, No. 8, Aug. 19, 1974, pp. 504, et seq.
Such prior art pulse train generators do not utilize the same circuit as in the preferred embodiment of the instant invention.
Further, typical TELD devices presently available have transit times ranging from 0.5 nanoseconds to 0.1 nanoseconds which are shorter than desired for clock pulses in some applications. Additionally, TELD's do not provide much power output in resistive circuits. If the TELD is incorporated into a tuned circuit, the power output is considerably improved. However, tuned circuits typically produce an output signal which is sinusoidal in nature, while in typical utilization devices for interval timing applications, a series of pulses of short duration compared to their period is desirable.